** A Floating Electromagnet [152]

A piece of iron placed in a coil of wire carrying a current of electricity becomes an electromagnet.  If such a coil and iron core be made small enough they can be attached to a cork and the cork, floating on a solution, will allow the magnet to point north and south.  The sketch shows how to make such an instrument.  A coil of insulated wire is wrapped around a small iron core, leaving a few inches of each end free for connections.  The insulation is removed

[Illustration:  Floating Electromagnet]

from these ends and they are run through a piece of cork.  Attach to the wires, on the under side of the cork, a piece of zinc to one end and a piece of copper to the other.  The cork is then floated on a solution of acid, with the zinc and copper hanging in the solution.  If zinc and copper are used, the solution is made from water and blue vitriol.  If zinc and carbon are used, the solution is made from sal ammoniac and water.

The float will move about on the solution until the magnet iron will point north and south.  If two of them are floating on the same solution, they will move about and finally arrange themselves end to end with the coils and magnet cores pointing north and south.  —­Contributed by C. Lloyd Enos.

** A Fish Bait [152]

A very effective fish bait is made by inclosing a live minnow in a short section of glass tube, which is filled with water and both ends closed with corks.  This is used in place of the spoon.

** Homemade Air Thermometer [152]

The illustration shows the complete thermometer.  The water in the glass tube is caused to rise and fall by the expansion and contraction of the air in the tin box.  A paper-fastener box, about 1-1/4 in.

[Illustration:  Air Thermometer]

deep and 2 in. in diameter will serve very well for the box A. Solder in the side of the box 1-in. piece of 1/4-in. brass tubing, B, and then solder on the cover, C, so that the only escape for the air is through the brass tube.  Secure a piece of 1/4-in. glass tubing — not shorter than 18 in.—­and bend it as shown at D in the sketch.  Hold the part of the tube to be bent in the broad side of a gas jet, and in a minute or two the tube will bend with its own weight.  Any angle can be given glass tubing in this way.  Connect the glass tube to B with a short piece of rubber hose, E. If the hose is not a tight fit, bind with a short piece of fine copper wire.  The standard, F, is made from a piece of No. 10 wire about 10 in. long.  To this standard solder the supporting wire, G—­No. 14 wire will do.  On one side bend the wire around the tube B, and on the other around the glass tube, D.

The base, H, can be made of oak, stained and varnished.  The bottom of the box, A, is covered with lampblack so as to readily absorb all heat that strikes the surface.  The black should not be put on until just before you paint the supports, cover and rim of the box with gold or silver paint.  Hold the bottom of the box to be blackened over a little burning cotton saturated with turpentine.